The long-term objectives of the proposal are to explore the nervous system changes underlying age-related deterioration in postural control and the integration of postural responses into voluntary movement such as gait and reaching. Statistics on falls in the elderly show that a high incidence of falls occur from a loss of balance while walking, climbing stairs or reaching for distant objects. We hypothesize that this is due to deterioration in postural muscle response synergies activated when balance is disturbed and to the integration of these responses into other movements. In order to test the hypothesis that there age-related changes in the characteristics of postural muscle response synergies activated during the gait cycle, balance of both young and older adults will be disturbed during different phases of the step cycle as they walk down a 4 meter walkway: a small platform incorporated into the walkway will move a small distance forward and backward to stimulate slipping unexpectedly. The organization of the postural adjustments will be compared for older and younger adults. Older adults also show an age-related deterioration in the anticipatory activation of postural muscles before voluntary movements. This could be due to 1) an age-related deterioration in nervous system postural function; or 2) a slowing of responses (due to other limitations, which causes a concomitant shift in response organization. Experiments will explore the effect of varying the speed of voluntary movements for both young and older adults in order to distinguish between these two possibilities. In order to determine if postural training allows older adults to reduce postural sway and optimize muscle response parameters when balancing under normal or changing task conditions, older adults will be given training in balance control under conditions of reduced or conflicting sensory output. The sort term practice effects and long term training effects will be determined. These studies will give us information on specific balance deficits and postural training effects in the elderly. This should lead to the creation of exercise and therapeutic remediation programs which are designed to improve individualized problems in balance control and gait. This will enhance the clinician's current more global and generalized approach to increasing physical fitness in the older adult.